A turbocharger may be coupled to an engine to improve engine output. The turbocharger increases engine output via providing compressed air to the engine. More specifically, an amount of fuel provided to the engine is increased as the amount of air provided to the engine increases so as to increase cylinder charge density, thereby increasing engine torque. However, a turbocharger may not be able to respond to changes in engine load as fast as is desired because of turbine inertia and pumping delays through the engine. One way to improve turbocharger response is to reduce a size of a turbine exhaust inlet. By reducing the turbine inlet size, the velocity of exhaust gas entering the turbine increases and improves turbocharger response. On the other hand, the efficiency of the turbine may be reduced at part load conditions where a waste gate of the turbocharger is at least partially open when the size of the turbine inlet is reduced. The partially open waste gate can lower exhaust pressure upstream of the turbine causing the turbine wheel to perform work on exhaust gas flowing through the turbocharger rather than the exhaust gas performing work on the turbine wheel.
The inventors herein have recognized the above-mentioned disadvantages for operating an engine having a turbocharger with a smaller turbine inlet and have developed a method for overcoming the disadvantages. The method comprises opening and closing a waste gate of a turbocharger synchronously with rotation of an engine.
By operating a waste gate synchronous with engine rotation, it may be possible to open the turbocharger waste gate so that excess exhaust flow can bypass the turbine while a portion of exhaust flow drives a turbine to increase engine and compressor output. Further, the waste gate can be closed when exhaust flow is reduced during a cylinder cycle so that more exhaust energy is transferred from the available exhaust flow to the turbocharger turbine during periods of lower exhaust flow. In this way, it may be possible to adjust exhaust flow through the turbine and waste gate in relation to when exhaust flow can be more efficiently utilized to provide a desired turbocharger output and efficiency.
The present description may provide several advantages. In particular, the approach may improve turbocharger efficiency. Further, the approach may enable use of turbochargers having smaller turbine inlets so that engine and turbocharger response may be improved. Additionally, in one example, the approach provides for the waste gate to be driven directly by the engine to simplify waste gate actuation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.